Design of a new soil concrete as an eco-material: Effect of clay and hemp fibers proportions

This study presents a series of soil concrete mix that is made of excavated soils, cement, lime and hemp fibers. An experimental program was carried out on the testing samples of soil concrete with different proportions of clayey soil and hemp fibers.

Journal of Science and Technology in Civil Engineering NUCE 2020 14 (1): 77–88 DESIGN OF A NEW SOIL CONCRETE AS AN ECO-MATERIAL: EFFECT OF CLAY AND HEMP FIBERS PROPORTIONS Ngo Duc Chinha,∗, Nguyen Ngoc Tanb a University of Transport and Communications, Cau Giay road, Dong Da district, Hanoi, Vietnam b Faculty of Building and Industrial Construction, National University of Civil Engineering, 55 Giai Phong road, Hai Ba Trung district, Hanoi, Vietnam Article history: Received 09/10/2019, Revised 03/11/2019, Accepted 11/11/2019 Abstract This study presents a series of soil concrete mix that is made of excavated soils, cement, lime and hemp fibers An experimental program was carried out on the testing samples of soil concrete with different proportions of clayey soil and hemp fibers This program focuses on several properties of soil concrete, such as compressive strength, autogenous shrinkage, drying shrinkage and water mass loss with time The obtained results show that the compressive strength of soil concrete increases even after 28 days, and can be reduced significantly with increasing the proportion of clayey soil The effect of clayey soil on the properties tested of soil concrete is more than that of hemp fibers In addition, drying shrinkage associated with water mass loss allows to describe the drying process of soil concrete Keywords: soil concrete; hemp fibers; compressive strength; autogenous shrinkage; drying shrinkage; water mass loss https://doi.org/10.31814/stce.nuce2020-14(1)-07 c 2020 National University of Civil Engineering Introduction The ecological aspect of building structures and the sustainable development is nowadays of high importance in the construction domain Therefore, building material containing a proportion of various ecological composition is a good idea Soil concrete is defined as an ecological building material since it uses a high content of clayey and sandy soils that are excavated directly at construction sites, and a small content of binders The aim of producing ecological concrete is to reduce CO2 emission, energy consumption in industry by limiting the use of cement and natural resources For instance, building made of low cost raw soils represents real interest since the acoustic and thermal properties of these materials are improved in comparison with ordinary concrete [1] The stabilization of soil in concrete can be realized by using different types of binders as lime and cement [2, 3] The addition of cement increases the evolution of the mechanical properties of concrete but can induce shrinkage and cracking [4] The use of natural fibers as hemp is particularly interesting as it minimizes the volume of waste in landfill It is renewable and environmentally friendly [5] Moreover, hemp is naturally produced, ∗ Corresponding author E-mail address: chinhnd@utc.edu.vn (Chinh, N D.) 77 Chinh, N D., Tan, N N / Journal of Science and Technology in Civil Engineering not require much energy to process, not require maintenance and consumes CO2 to grow, making the hemp concrete as a carbon negative building material The addition of hemp fibers can also reduce the density, shrinkage and cracking of soil concrete and improve the thermal properties [6, 7] The acoustic and thermal properties of soil concrete could be better than ordinary concrete, which are explained by the use of clayey soil and hemp fibers [8] Concrete volume change is an unavoidable phenomenon, from very early age to long-term behavior [9] and more particularly with soil concrete containing a high proportion of fines aggregates [10, 11] Autogenous shrinkage is defined as a concrete volume change occurring without moisture transfer to the environment It depends mainly on the composition of concrete and develops more rapidly with time than drying shrinkage [12] Drying shrinkage depends on the age of the beginning of drying and external parameters such as relative humidity and specimen size Thus, the understanding of shrinkage process and more particularly drying shrinkage, known as the main cause of micro and macro cracking, is essential In this study, the design of soil concrete mix is presented, which made of clayey soil, sandy soil, hemp fibers, cement and lime A series of soil concrete mix has been proposed for considering different proportions of clay soil and hemp fibers In the laboratory, an experimental program carried out on the testing samples of soil concrete The experimental data allow to determine the compressive strength at 7, 28 and 180 days, autogenous shrinkage, drying shrinkage and water mass loss with time of soil concrete The obtained results are also used to evaluate the effect of clayey soil and hemp fibers on these physical and mechanical properties of soil concrete Experimental program 2.1 Materials used In this study, the soil concrete was made of different compositions, such as soil, cement, lime and hemp fibers The soils used were excavated at two construction sites in Bordeaux city, France during the execution of underground These soils can be classed into two principal types: (a) clayey soil, (b) sandy soil a Clayey soil In the laboratory, some tests such as the Atterberg limits, particle-size analysis and the methylene blue were carried out on the samples in order to determine the type of used clayey soil (Fig 1) according to the unified soil classification system in the American standard ASTM D2487-17 [13] The experimental results are synthesized in Table for the parameters of soil: liquid limit WL , plastic limit WP , plasticity index IP , granulometric composition, and VBS that is the methylene blue value of the total soil These results show that the used soil can be defined as low plastic clay (CL) and has a high content of silt particles b Sandy soil In the laboratory, some tests such as the particle-size analysis, methylene blue, specific density and fineness modulus were performed on the samples in order to determine the type of used sandy soil Fig presents the sandy soil after grinding by a rubber hammer The experimental results are synthesized in Table These results show that the used soil can be defined as poorly graded sand with gravel according to the unified soil classification system in the American standard ASTM D2487-17 [13] 78 Chinh, N D., Tan, N N / Journal of Science and Technology in Civil Engineering Figure Clayey soil after grinding Figure Sandy soil after grinding Table Characteristics of used clayey soil Test Criterion Value USCS* [13] Low plastic clay (CL) Atterberg limits (%) Liquid limit WL Plastic limit WP Plasticity index IP 51.74 30.08 21.66 Particle-size analysis (%) Clay (< 0.002 mm) Silt (0.002 – 0.06 mm) Sand (0.06 – mm) Gravel (> mm) 25.06 55.94 19 Methylene blue VBS 5.72 Lean clay (CL) *USCS: The Unified Soil Classification System is a soil classification system used in engineering and geology to describe the texture and grain size of a soil Table Characteristics of used sandy soil Test Criterion Value Particle-size analysis (%) Silt (0.002 – 0.06 mm) Sand (0.06 – mm) Gravel (> mm) VBS 0.64 72.54 26.82 0.67 2.33 2.57 Blue methylene Specific density (kg/m3 ) Fineness modulus USCS* [13] Sandy soil Poorly graded sand with gravel (SP) c Hemp fibers In this study, hemp fibers were used as an additional composition for improving the tensile strength of soil concrete The hemp fibers have been often used among the natural fibers with low price, such as like sisal, jute, rice husk, flax, bamboo, banana fiber, oil palm fiber, sugarcane bagasse, wood fiber, etc [14] The diameter of these fibers is less than mm, and the length ranging from 79 Chinh, N D., Tan, N N / Journal of Science and Technology in Civil Engineering to 25 mm The density of hemp fibers is about 100 kg/m3 in the ambient conditions The thermal conductivity is equal to λ = 0.05 W/m.K The tensile strength varies between 300 and 1100 MPa The hemp fibers are highly hydrophilic and can absorb water up to 2.5 times of their mass d Cement The Portland cement CEM V/A (S-V) 42.5N according to the European standard EN 197-1 was used as the first binder of soil concrete This cement has been chosen since it has two important criterias as clinker ratio and CO2 impact The compositions of the cement are provided by the manufacturer and presented in Table In the tested soil concrete mixes, the cement content has been used ranging from 125 to 155 kg/m3 Table Composition of cement Main composition (% by mass) Cement Portland clinker Blast furnace cinder Fly ash 40 – 64 18 – 30 18 – 30 CEM V/A (S-V) Additional composition 0–5 e Lime In the soil concrete mix, the lime can also be used as the second binder in order to reduce the cement content In this study, the pure natural lime named 100 NHL5 according to the European standard EN 459 was used that has no additives The specific density of the lime used is 700 kg/m3 In the tested soil concrete mixes, the lime content has been used about 40 kg/m3 2.2 Soil concrete mix The design of soil concrete mix aims to increase the clayey soil content while decreasing the sandy soil content For this purpose, the clayey soil content was varied from 0%, 20%, 30% and 40% in the mass total of the soil, named 0A, 20A, 30A and 40A, respectively For each clayey soil content, the volume fraction of hemp fibers was mixed ranging 0%, 0.6% and 1.2% in mass, named 0F, 0.6F and 1.2F, respectively In this study, 12 soil concrete mixes studied were presented in Table In fact, when increasing the proportion of clayey soil from to 40%, the cement content can be reduced from 158.1 to 126.6 kg/m3 , meanwhile the water content must increase for the workability in the mixing The casting of concrete mixtures has been realized by vibration, as normal concrete, to obtain the requirement of workability on construction sites After mixing soil concrete, the consistence was measured by the slump test and ranging from 65 to 165 mm in function of the proportion of clayey soil and hemp fibers 2.3 Compression test The compression test aims to determine the compressive strength of soil concretes that were made of different mixes as presented in Table The Young’s modulus of soil concretes can be also determined from the stress – strain curve The results of this test can be used to assess the effect of clay and hemp fibers on the soil concrete compressive strength at the target age This test was carried out on the cubic samples with the dimensions of 100×100×100 mm Fig shows the compression test that carried out on a typical sample of soil concrete During the test, four devices were installed at the center of the lateral faces of each sample, two devices for measuring the vertical displacement, and two another for measuring the horizontal displacement The axial load was applied on the sample with the constant speed of 0.5 mm/minute 80 Chinh, N D., Tan, N N / Journal of Science and Technology in Civil Engineering Table Soil concrete mix studied in the laboratory No Soil Clayey soil concretemix (kg/m3 ) 10 11 12 0A0F 0A0.6F 0A1.2F 20A0F 20A0.6F 20A1.2F 30A0F 30A0.6F 30A1.2F 40A0F 40A0.6F 40A1.2F 0.0 0.0 0.0 247.8 241.4 236.6 368.3 356.3 345.3 501.1 476.6 454.4 Sandy soil (kg/m3 ) 1386.8 1306.2 1238.2 991.4 965.7 946.7 859.5 831.5 805.7 751.7 714.9 681.6 Cement Lime (kg/m3 ) (kg/m3 ) 151.8 144.3 138.0 135.6 133.3 131.9 134.4 131.2 128.3 137.1 131.6 126.6 45.0 42.8 40.9 40.2 39.5 39.1 39.9 38.9 38.1 40.7 38.8 37.6 Hemp fibers (kg/m3 ) 0.0 12.0 22.9 0.0 11.1 21.9 0.0 10.9 21.3 0.0 10.9 21.0 Water Slump (kg/m3 ) (mm) 330.6 314.2 300.6 398.9 392.1 388.0 417.6 407.7 398.7 466.1 447.3 430.5 165 162 157 105 148 95 95 65 140 125 73 105 Figure Compression test on the cubic sample of soil concrete 2.4 Shrinkage and water loss measurements As soil concrete presents a high volumetric change that can cause the infiltration of water and impact its durability, the measurements of shrinkage were carried out on the prismatic samples of the dimensions 40×40×160 mm exposed to controlled ambient conditions with the temperature of 20◦C and the relative humidity of 60% All samples were overlaid by a thin plastic sheet at the top of sample mold during 24 first hours in order to prevent water loss Then, the samples were demolded, including two types: (i) uncovered samples for drying shrinkage test and mass loss test (Fig 4(a)); (ii) covered samples by self-adhesive aluminum paper for autogenous shrinkage test (Fig 4(b)) Fig 4(c) presents the shrinkage test that was carried out on uncovered samples for determining the total shrinkage of soil concrete The longitudinal deformation of each sample is measured by a displacement device (LVDT) The shrinkage of each sample is calculated by the ratio between the 81 Chinh, N D., Tan, N N / Journal of Science and Technology in Civil Engineering (a) Uncovered samples of soil concrete (b) Covered samples of soil concrete (c) Shrinkage measurement Figure Shrinkage and mass loss measurements of soil concrete samples absolute deformation and the length of sample The shrinkage of each soil concrete is the average value of three samples In this study, six soil concrete mixes having three proportions of clayey soil ranging from 0%, 20% and 40%, and two proportions of hemp fibers of 0% and 1.2% were measured the shrinkage and mass loss in function of time There were the total of 36 samples tested At the same time, the mass loss was measured on the uncovered samples for a better understanding of drying shrinkage phenomenon The measurements of mass loss were performed by the electronic balance with 0.01 gram readability The mass loss is calculated in percentage by the ratio between the water loss mass by evaporation and the initial mass of sample Results and discussions 3.1 Compressive strength of soil concrete For each soil concrete mix, three cubic samples with the dimensions of 100×100×100 mm were tested to determine the average value of the compressive strength, as well as the standard deviation and the coefficient variation The experimental results of compressive strength are presented in Figs 5, and for 12 soil concretes at 7, 28 and 180 days, respectively In this study, 36 sets of soil concrete samples were tested At days, 12 sets of tested soil concrete samples show that the average values of compressive strength range from 0.5 to 1.2 MPa (Fig 5) The compressive strength of soil concrete decreases significantly with increasing the proportion of clayey soil The effect of hemp fibers on the compressive strength is only observed for the soil concrete without clayey soil (100% sandy soil) This effect is negligible for soil concrete having clayey soil At 28 days, the average values of soil concrete compressive strength range from 1.0 to 2.4 MPa (Fig 6) The same remarks are idenfied on the effect of the proportion of clayey soil and hemp fibers The compressive strength can be reduced to MPa with beyond 20% clayey soil Meanwhile, it can be reduced from 0.5 to 0.8 MPa with the hemp fibers contents of 0.6 - 1.2% The effect of hemp fibers on the compressive strength may be due to the lower density and the modification of the soil concrete structure and pore distribution by introducing voids and discontinuity At 180 days, the compressive strength of soil concrete increases about two times in comparison to that at 28 days The average values of compressive strength range from 2.5 to 5.1 MPa (Fig 7) The evolution of soil concrete compressive strength occurs in more time in comparison to ordinary concrete that is normally characterized the mechanical properties at 28 days Fig shows the evolution of compressive strength of 12 soil concrete mixes during 180 first days The obtained results allow to quantify the effect of curing time on the compressive strength of soil concrete These results show 82 Compressive strength (M concrete samples show that the 1.0 concrete average values of compressive 0.8 range from 1.2 MPa of 0.6 mix, three strength cubic samples with0.5theto dimensions 0.4 (Figure 5) The compressive strength Chinh, N D., Tan, N / compressive Journal of Science and Technology in Civil Engineering o determine the average value of N.the Chinh,0.2 N D., Tan, N N / Journal of Science and Technology in Civil Engineering of soil concrete decreases that the compressive strength of soil concrete increases ard deviation and the coefficient variation The 0.0 even after one month This is an important strengthterm, can be reduced to 10 MPa with strength significantly with theshort mechanical property soilincreasing concrete In the the compressive of soil concrete is 0.6 1.2 ve strength are presented inofFigures 5, 6, for 12 soil20% clayey Hemp fibers content (%) beyond soil Meanwhile, mainly associated to the cement hydration Meanwhile, in the long term, it may be provided by the proportion of clayey soil The effectit can be reduced from 0.5 to 0.8 MPa respectively In this study, 36pozzolanic sets of soil concrete hydration reaction and the reactions between clay minerals and calciumstrength hydroxide Figure Compressive offormed soil with the hemp fibers contents of 0.6 of hemp fibers on the compressive by the cement hydration [15] 1.2% The effect of hemp concrete fibers on at days strength is only observed for the soil the compressive strength may be due 1.4 2.8 the lower density and the 0A 20A 30A 40A 0A 20A 30A 40A d soil concrete without clayey soil (100%tomodification 1.2 2.4of the soil concrete the sandy soil) This effect is negligiblestructure and2.0 pore distribution by Figure Compressive strength of soil 1.0 introducing voids and discontinuity concrete at 180 days ssive for 0.8 soil concrete having clayey soil 1.6 At 180 days, the compressive strength of soil concrete increases about two times MPa 0.6 At 28 days, the average valuesin comparison1.2to that at 28 days The average values of compressive strength range from 0.4 2.5 to 5.1 MPa 0.8(Figure 7) The evolution of soil concrete compressive strength occurs ength of soil concrete compressive strengthin more time in comparison to ordinary concrete that is normally characterized the 0.2 0.4 eases mechanical properties at 28 days Figure shows the evolution of compressive strength range from 1.0 to 2.4 MPa (Figure 6) 0.0 of 12 soil concrete 0.0 mixes during 180 first days The obtained results allows to quantify the 0.6 1.2 compressive strength 0.6 of soil concrete 1.2These results show the effect of curing time on the The same0remarks are idenfied on the Hemp fibers content (%) Hemp fibers content (%) that the compressive strength of soil concrete increases even after one month This is an ffect effect of the proportion of clayey soilimportant mechanical property of soil concrete In the short term, the compressive Figure Compressive strength of soil Figure strength of soil concrete Figure Compressive strength of soil concrete Figure 5.Compressive Compressive strength of soil urnal and Technology in Civil Engineering ssiveof Science strength of soil concrete is mainly associated to the cement hydration Meanwhile, in and hempconcrete fibers compressive at days at 28atdays concrete 28reaction daysand the pozzolanic reactions atThe days the long term, it may be provided by the hydration e soil between clay minerals and calcium hydroxide formed by the cement hydration [15] 2.8 0A 20A 30A 40A 6.0 00% 6.0 with 0A0F 0A0.6F 0A1.2F 2.4 0A 20A 30A 40A 20A0F 20A0.6F 20A1.2F gible 5.0 while, 5.0 30A0F 30A0.6F 30A1.2F 2.0 40A0F 40A0.6F 40A1.2F oil MPa 4.0 4.0 1.6 0.6 1.2 3.0 3.0 alues 0.8 rs on 2.0 2.0 ength 0.4 e due 1.0 1.0 re 6) 0.0 the 0.0 0.6 1.2 0.0 n the 0.6content (%) 1.2 Hemp fibers 30 60 90 120 150 180 210 crete Hemp fibers content (%) Time (day) y soil Figure Compressive strength of soil n by Figure Evolution of soil concrete strength with time Figure 7.7.Compressive strength of soil concrete Figure Evolution of soilcompressive concrete compressive ssive Figure Compressive concrete atdays 28strength days of soil at 180 strength with time uity concrete at 180 days 6.0 Compressive strength (MPa) 0A 20A 30A 40A 5.0 4.0 3.0 2.0 1.0 0.0 1.2 Compressive strength (MPa) 0.6 Hemp fibers content (%) Compressive strength (MPa) (MPa) strength Compressive (MPa) strength Compressive Compressive strength (MPa) 1.0 to 2.4 MPa at 28 The measured compressive strength of soil concrete is low ranging from 7days ive strength ofcompared soil concrete increases aboutThe two times with ordinary concrete range of compressive strength is acceptable regarding the application this kind of concrete which is used as a filling concrete and not for assuring high load The average values ofofcompressive strength range from capacity (e.g wall, block, etc.) This is due to low cement content, the higher porosity of soil concrete volution of soil concrete compressive strength occurs constituted of fine grained mixtures and the higher water content required to achieve an acceptable ordinary concrete workability.that is normally characterized the Figure shows the evolution of compressive strength 3.2 Young’s modulus of soil concrete 180 first days The obtained results allows to quantify Fig shows the typical diagram of stress – strain that presents the relationship between commpressive pressive strengthstrength of soiland concrete These results show deformations of the soil concrete mix named both longitudinal and horizontal oil concrete increases even after one month This is an 83 of soil concrete In the short term, the compressive y associated to the cement hydration Meanwhile, in by the hydration reaction and the pozzolanic reactions 3.2 Young’s modulus of soil concrete Figure shows the typical diagram of stress – strain that presents the relationship between compressive strength and both longitudinal and horizontal deformations of the soil concrete mix named 40A1.2F having 40% clayey soil and 1.2% hemp fibers at 7, Chinh, N D., Tan, N N / Journal of Science and Technology in Civil Engineering 28, and 180 days Young’s modulus is calculated by the slope of the curve between 10% 40A1.2F having clayey soil and 1.2% hemp The fibers at 7, 28,results and 180 days Young’s modulus is and 30% of 40% ultimate compressive strength obtained show that the Young’s calculated by the of the curve betweenwith 10%aand 30% of even ultimate compressive The obmodulus of slope soil concrete increases high rate after 28 days strength The elastic tained results show that the Young’s modulus of soil concrete increases with a high rate even after 28 modulus of tested soil concrete increases from GPa at days to GPa at 180 days days The elastic modulus of tested soil concrete increases from GPa at days to GPa at 180 days stress-strain curves ofconcrete soil concrete a higher ductility with increasing the The The stress-strain curves of soil showshow also aalso higher ductility with increasing the proportion proportion of clayey soil Moreover, the addition ofreinforcement hemp fibers asinreinforcement in soil of clayey soil Moreover, the addition of hemp fibers as soil concrete can prevent horizontal deformation during compression loading.during compression loading concrete can prevent horizontal deformation Compressive strength (MPa) 3.0 2.5 2.0 days 28 days 1.5 180 days 1.0 0.5 0.0 -0.02 -0.01 0.00 Horizontal deformation (%) 0.01 0.02 0.03 Longitudinal deformation (%) 0.04 Figure 9 Compressive strength in function of longitudinal and horizontal deformationsdeformations of soil concrete Figure Compressive strength in function of longitudinal and horizontal of soil concrete 3.3 3.3 Shrinkage of soil Shrinkage of concrete soil concrete Fig 10 presents the evolution of autogenous shrinkage of soil concrete having 0%, 20%, 40% Figure 10 presents the evolution of autogenous shrinkage of soil concrete having clayey soil and 0%, 1.2% hemp fibers during 70 first days The autogenous shrinkage of soil concrete 0%, 20%, clayey soiltheand hemp fibers gradually during 70in first days The Auincreases with a 40% high rate during three0%, first1.2% days and decreases function of time autogenous shrinkage of soil concrete increases withloss a high during three shrinkage first togenous shrinkage occurs independently of external water and israte a result of the chemical and decreases gradually in of function ofintime Autogenous shrinkage occurs and days self-drying shrinkage The reduction humidity the pore system causes water–air meniscus that subjects the pore walls to considerable stress and leads to substantial self-drying shrinkage The obtained results show that the autogenous shrinkage of soil concrete without hemp fibers increases with the proportion of clayey soil The autogenous shrinkage of soil concrete having 40% clayey soil and 0% hemp fibers (40A0F) at 67 days increases about four times in comparison with that of soil concrete having 20% clayey soil (20A0F) and 0% clayey soil (0A0F), 1900 µm/m versus 450 µm/m The addition of 1.2% hemp fibers causes a slight increase of autogenous shrinkage for soil concrete having 20% and 0% clayey soil (20A1.2F and 0A1.2F) However, the autogenous shrinkage of soil concrete having 40% clayey soil and 1.2% hemp fibers (40A1.2F) decreases significantly in comparison to that of soil concrete having 40% clayey soil and 0% hemp fibers (40A0F) This difference may be related to the variation of the global porosity between soil concrete mixes and the water absorption of hemp fibers [16, 17] The autogenous shrinkage of soil concrete having 1.2% hemps fibers is in the range of 600 – 800 µm/m In general, the drying shrinkage is defined as the contracting of a hardened concrete mixture due to the loss of capillary water This shrinkage causes an increase in tensile stress, which may 84 clayey soil and 0% hemp fibers (40A0F) This difference may be related to the variation of the global porosity between soil concrete mixes and the water absorption of hemp fibers [16, 17] The autogenous shrinkage of soil concrete having 1.2% hemps fibers is in the rangeChinh, of 600 – 800 µm/m N D., Tan, N N / Journal of Science and Technology in Civil Engineering 0A0F 0A1.2F 20A0F 20A1.2F 40A0F 40A1.2F Autogenous shrinkage (µm/m) 2000 1600 1200 800 400 0 10 20 30 40 50 Time (day) 60 70 80 90 Chinh, N D., Tan, N N / of Journal of Science and Technology in Civil Engineering Figure 10 Autogenous shrinkage soilofconcrete with different contents ofcontents clay and of hemp Figure 10 Autogenous shrinkage soil concrete with different clayfibers and hemp fibers atthe the drying beginning andstructure, laterisstabilizes 10 and 15 days effect lead increases to cracking, deterioration of concrete before between thethe concrete is subjected to any kind of In quickly general, shrinkage defined as contracting of a The hardened loading Fig 11 presents the evolution of drying shrinkage of soil concrete having 0%, 20%, of the proportion of clayey the dryingwater shrinkage is significant Foranexample, concrete mixture due to the soil loss on of capillary This shrinkage causes increasefor in40% clayey and 0%,having 1.2% hemp fibers during 70 first days The fibers drying(40A1.2F) shrinkage isthe calculated by soilsoilconcrete 40% clayey soil and 1.2% hemp drying tensile stress, which may lead to cracking, deterioration of concrete structure, before the the subtraction of the autogenous shrinkage from the total shrinkage The drying shrinkage of soil shrinkageisreach a high any value about 11800 µm/m, corresponding to approximately concrete subjected kind of loading Figure 11 presents of drying concrete increases quickly to at the beginning and later stabilizes betweenthe 10evolution and 15 days The effect times higher than that of soil concrete having 0% clayey soil (0A1.2F and 0A0F) The shrinkage of of soil concrete having 0%, 20%, 40% is clayey soil and 1.2% hemp of the proportion clayey soil on the drying shrinkage significant For0%, example, for soilfibers concrete effect of hemp fibers on the drying shrinkage depends also on the proportion having 40% 70 clayey and The 1.2%drying hemp fibers (40A1.2F) the drying reachofa clayey highthevalue during firstsoil days shrinkage is calculated byshrinkage the subtraction of soil in the ofshrinkage soil concrete In fact, the drying shrinkage increases for aboutautogenous 11800 µm/m, corresponding to approximately times higher than that ofsignificantly soil concrete having frommix the total shrinkage The drying shrinkage of soil concrete 0% clayey soil (0A1.2F and 0A0F) The effectwith of hemp on the drying40% shrinkage soil concrete of 40A1.2F in comparison that fibers of 40A0F having clayeydepends soil andalso on the of clayey soil in concrete mix In fact, the drying shrinkage increases 0%proportion hemp fibers This may bethe dueoftosoil modification in pore system structure and transfer significantly for soil concrete of 40A1.2F in comparison that of 40A0F having 40% clayey soil 10 at thewith properties that modify the water evaporation surface of soil concrete 0A0F 0A1.2F 20A0F 20A1.2F 40A0F 40A1.2F Drying shrinkage (µm/m) 12000 10000 8000 6000 4000 2000 0 10 20 30 40 50 Time (day) 60 70 80 90 Figure Drying shrinkage shrinkage ofofsoil concrete withwith different contents of clay and hempand fibers Figure 11.11.Drying soil concrete different contents of clay hemp fibers 3.4 Water mass loss 85 The water mass loss of soil concrete was also measured at the same time of the measurement of drying shrinkage The obtained results are presented in Figure 12 for Chinh, N D., Tan, N N / Journal of Science and Technology in Civil Engineering and 0% hemp fibers This may be due to modification in pore system structure and transfer properties that modify the water evaporation at the surface of soil concrete 3.4 Water mass loss The water mass loss of soil concrete was also measured at the same time of the measurement of drying shrinkage The obtained results are presented in Fig 12 for soil concrete with 0%, 20%, 40% clayey soil and 0%, 1.2% hemp fibers The variation of water mass loss transcribes the diffusion capacity of the material The mass loss is important during 15 first days and later stabilizes The water mass loss with time shows similar trend as the drying shrinkage The water mass loss increases when rising the proportion of clayey soil, which could explain the increase of drying shrinkage The addition of hemp fibers causes the increase of the water mass loss for soil concrete having 0% and 20% clayey soil (0A1.2F Meanwhile, causes the decrease the water mass loss for Chinh, N D.,and Tan,20A1.2F) N N / Journal of Scienceitand Technology in CivilofEngineering soil concrete having 40% clayey soil (40A1.2F) 0A0F 0A1.2F 20A0F 20A1.2F 40A0F 40A1.2F 25 Mass loss (%) 20 15 10 0 10 20 30 40 50 Time (day) 60 70 80 90 Figure 12.12 Evolution massloss lossofof concrete Figure Evolutionof of water water mass soilsoil concrete Drying shrinkage deformation (µm/m) The water mass loss has 0A0F a good 0A1.2F correlation with the drying shrinkage of tested soil concretes 20A0F 20A1.2F 40A0F 40A1.2F Fig 13 presents the relationship between these two parameters for six tested soil concrete mixes 12000 There are some phases that can be distinguished in Fig 13 In the first phase called “dormant zone”, 10000 the water loss without shrinkage is observed on the tested samples of soil concrete In fact, the water content gradient in soil concrete due to drying generates a stress gradient, so a high tensile stress at 8000 the sample surfaces exposed to the atmosphere and causes cracks The surface area to volume ratio is an important factor 6000 in this phase During the second phase, the gradients become more pronounced, the cracks at the surface remains unchanged The drying shrinkage is proportional to water mass loss (linear zone), with 4000 a slope that reflects the fineness of the porous network In the last phase, a stabilisation phase is observed with a lower shrinkage rate Soil concrete shrinkage is higher in 2000 concrete due to the lack of coarse aggregates that inhibit the total shrinkage comparison to ordinary and the higher porosity related to incorporating clayey soil and high water content 0 10 15 Mass loss (%) 20 25 Figure 13 Correlation between drying shrinkage and water mass loss of soil concrete 86 The water mass loss has a good correlation with the drying shrinkage of tested soil concretes Figure 13 presents the relationship between these two parameters for six tested soil concrete mixes There are some phases that can be distinguished in Figure 0 10 20 30 40 50 Time (day) 60 70 80 90 Figure 12 Evolution of water mass loss of soil concrete Drying shrinkage deformation (µm/m) Chinh, N D., Tan, N N / Journal of Science and Technology in Civil Engineering 0A0F 0A1.2F 20A0F 20A1.2F 40A0F 40A1.2F 12000 10000 8000 6000 4000 2000 0 10 15 Mass loss (%) 20 25 13 Correlation between drying shrinkage and water mass loss of soil concrete FigureFigure 13 Correlation between drying shrinkage and water mass loss of soil concrete The water mass loss has a good correlation with the drying shrinkage of tested Conclusions soil concretes Figure 13 presents the relationship between these two parameters for six The present study aims to consider series of phases soil concrete mixes with different in proportions tested soil concrete mixes There aare some that can be distinguished Figure of clayey soil (0%, 20%, 30%, 40%) and hemp fibers (0%, 0.6%, 1.2%) The experimental results 13 In the first phase called “dormant zone”, the water loss without shrinkage is observedallow to evaluate the effect of clayey soilconcrete and hempInfibers physicalgradient and mechanical properties of on the tested samples of soil fact, on theseveral water content in soil concrete soil concrete, such as compressive strength, Young’s modulus, autogenous shrinkage, drying shrinkdue to drying generates a stress gradient, so a high tensile stress at the sample surfaces age and water mass loss exposed thetheatmosphere causes The surface area1.0 to to volume ratio an and For tested to mix, compressiveand strength of cracks soil concrete ranges from 2.4 MPa at 28isdays important factor this phase During second phase, the2.5 gradients become increases even after oneinmonth with the averagethe values ranging from to 5.1 MPa at 180more days The results show that the strength of soil concrete decreases when increasing the proportion pronounced, thecompressive cracks at the surface remains unchanged The drying shrinkage is of clayey soil and hemp fibers, which could be related to increasing concrete porosity The proportional to water mass loss (linear zone), with a slope that reflects the fineness ofeffect of clayey soil is higher than hemp fibers The hemp fibers cause a slight reduction of compressive strength that is due to lower density and modification of soil concrete structure and pore system by 12 introducing voids and discontinuity The soil concrete deformation due to autogenous and drying shrinkage increases significantly when rising the proportion of clayey soil, especially with the use of 40% clayey soil of the total mass of soils used The drying shrinkage increases reaches important value for soil concrete having 40% clayey soil, which corresponds to about times higher than that without clayey soil The addition of 1.2% hemp fibers influences slightly the shrinkage of soil concrete that has less than 20% clayey soil Meanwhile, it causes a significant increase of drying shrinkage for soil concrete having 40% clayey soil Thus, the obtained results show that it recommends to use less than 40% clayey soil and 1.2% hemps fibers in order to design the soil concrete mix as a building material References [1] Van Damme, H., Houben, H (2018) Earth concrete Stabilization revisited Cement and Concrete Research, 114:90–102 [2] Rao, S M., Shivananda, P (2005) Compressibility behaviour of lime-stabilized clay Geotechnical & Geological Engineering, 23(3):309–319 87 Chinh, N D., Tan, N N / Journal of Science and Technology 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hurds composites Chemical Engineering, 39:559–564 88 ... sample of soil concrete 2.4 Shrinkage and water loss measurements As soil concrete presents a high volumetric change that can cause the infiltration of water and impact its durability, the measurements... evaluate the effect of clayey soil and hemp fibers on these physical and mechanical properties of soil concrete Experimental program 2.1 Materials used In this study, the soil concrete was made... increase of drying shrinkage The addition of hemp fibers causes the increase of the water mass loss for soil concrete having 0% and 20% clayey soil ( 0A1 .2F Meanwhile, causes the decrease the water